Videocheck search path fix for "-c" handle limit (#1692)

Tested against dev DB and dev-c2g bucket.  See in log below how -c correctly limits class now:


```
./manage.py videocheck
Videos found in database: 14 
Bucket: dev-c2g
	videos found: 190
	manifests found: 83
	small formats found: 13
	large formats found: 6
in database, but not in storage: 14
in database and storage, but no thumbnails: 0
in database and storage, but no small format: 0
in database and storage, but no large format: 0
==================================
# missing video file "default" for networking Fall2012 intro 
# missing video file "default" for networking Fall2012 ngrams 
# missing video file "default" for networking Fall2012 regexp_in_practical_nlp 
# missing video file "default" for crypto Fall2012 regexp_in_practical_nlp 
# missing video file "default" for crypto Fall2012 ngrams 
# missing video file "default" for crypto Fall2012 intro 
# missing video file "default" for networking Fall2012 computing_min_edit_distance 
# missing video file "default" for networking Fall2012 regexp 
# missing video file "default" for crypto Fall2012 computing_min_edit_distance 
# missing video file "default" for crypto Fall2012 tokenization 
# missing video file "default" for networking Fall2012 tokenization 
# missing video file "default" for networking Fall2012 min_edit_distance 
# missing video file "default" for crypto Fall2012 regexp 
# missing video file "default" for crypto Fall2012 min_edit_distance 
sef@seldon (sef-1692-videocheck $) ~/src/class2go/main> ./manage.py videocheck -c "crypto--Fall2012"
Videos found in database: 7 
Bucket: dev-c2g
	videos found: 0
	manifests found: 0
	small formats found: 0
	large formats found: 0
in database, but not in storage: 7
in database and storage, but no thumbnails: 0
in database and storage, but no small format: 0
in database and storage, but no large format: 0
==================================
# missing video file "default" for crypto Fall2012 min_edit_distance 
# missing video file "default" for crypto Fall2012 regexp_in_practical_nlp 
# missing video file "default" for crypto Fall2012 ngrams 
# missing video file "default" for crypto Fall2012 intro 
# missing video file "default" for crypto Fall2012 tokenization 
# missing video file "default" for crypto Fall2012 computing_min_edit_distance 
# missing video file "default" for crypto Fall2012 regexp 
sef@seldon (sef-1692-videocheck $) ~/src/class2go/main> ./manage.py videocheck -c "networking--Fall2012"
Videos found in database: 7 
Bucket: dev-c2g
	videos found: 0
	manifests found: 0
	small formats found: 0
	large formats found: 0
in database, but not in storage: 7
in database and storage, but no thumbnails: 0
in database and storage, but no small format: 0
in database and storage, but no large format: 0
==================================
# missing video file "default" for networking Fall2012 intro 
# missing video file "default" for networking Fall2012 ngrams 
# missing video file "default" for networking Fall2012 regexp_in_practical_nlp 
# missing video file "default" for networking Fall2012 computing_min_edit_distance 
# missing video file "default" for networking Fall2012 regexp 
# missing video file "default" for networking Fall2012 tokenization 
# missing video file "default" for networking Fall2012 min_edit_distance 
```